JP2002-115571A, published by the Japan Patent Office in 2002, discloses a variable compression ratio device that connects a piston and a crankshaft of an internal combustion engine via a plurality of links so as to vary the compression ratio of the internal combustion engine. In this prior art device, the piston and the crankshaft are connected via an upper link and a lower link, and by varying the tilt of the lower link, the compression ratio is varied. The tilt of the lower link is varied using the following mechanism.
One end of a control link is connected to the lower link, and another end of the control link is connected to a control shaft, which is substantially parallel to the crankshaft, in an eccentric position. With this constitution, when the control shaft is rotationally displaced, the control link varies the tilt of the lower link.
A control plate that rotates integrally with the control shaft is provided to displace the control shaft rotationally, and a connecting pin inserted into an elongated hole formed in the control plate is driven by a linear actuator.